Letha P Cheriyan^1,, Harish R², R. Steffy¹

Pristine natural freshwater resources being severely contaminated by microbiological pollutants is still a big issue in many parts of the world. In the present study, water samples taken from the upstream, midstream, and downstream reaches of the Meenachil River were analysed for the presence of microbial pollution indicators such as faecal coliforms (FC), faecal streptococci (FS), and Eschericia coli. The E. coli isolates were subjected to antimicrobial susceptibility tests and the multiple antibiotic resistance (MAR) indexes were calculated so as to delineate the potential risk posed by infections to humans and animals using the river for routine potable and recreational purposes. E. coli was consistently isolated from all the samples collected from the different zones of the river. Other faecal coliforms such as Klebsiella oxytoca, Citrobacter koseri, Enterobacter, Proteus vulgaricus, and Shigella boydii were also identified. Higher FC/FS ratios were noticed for the midstream and the downstream sites indicating the contamination from high-risk sources such as human and anthropogenic domestic wastes. The MAR index values of E. coli isolates ranged from 0.33 upstream, 0.416 for midstream and 0.583 for the downstream reaches. Given that E. coli is an ideal indicator of faecal pollution, their existence and extended survival of multiple antibiotic resistance natural freshwater pose a potential risk for the consumers. Rapid urbanization and resultant waste drainage in the downstream stretches of the river might have accelerated the deterioration of the water quality up to a certain extent. Furthermore, the riverine system as it flows downstream loses its self-purification capacity due to the loss of natural water drifts. This may be attributed to the periodic shutdown of the salinity barrier, Thanneermukkam Bund in the confluence zone of the river which results in a temporary stagnation of the running waters in the lower stretches.

antibiotic resistance, aquatic environment, Faecal coliforms, sewage, pollutants